Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

APPLICATIONS OF NITRILE OXIDES 105
Anthracene-9,10-dicarbonitrile oxide has been used for cross-linking of cyano
group-containing poly(arylene sulÞdes) (520). Acrylic polymers containing nitrile
groups do not possess typical curing sites such as double bonds. Addition of stable
bis(nitrile oxide) to the acrylic polymer, causes cross-linking at a low-temperature.
Heat-resistant thermoplastic vulcanizates with high resistance to solvents and
increased compression resistance are formed (521).
Nitrile oxides have been used as reagents for heat activated cross-linking
of polymers having appropriate functionality, such as alkenes, alkynes, nitriles,
and isocyanates. The use of nitrile oxide compounds are in Þlled or unÞlled
applications such as pressure sensitive adhesives, reactive hot melts, polyurethane
dispersions, thermosetting adhesives, thermoplastic adhesives and coatings (522,
523). Formulations containing stable nitrile oxide reagents have been developed
for coatings, composites, and moldings (524).
Aqueous polynitrile oxide curing compositions, with good storage stability,
have been patented (525). The compositions comprise aqueous dispersions containing
nitrile oxides and are useful for coating systems that are cured at room
temperature without the release of byproducts. Latexes are cured by mixing a
polymer latex with a stable polynitrile oxide, for example, 2,4,6-triethylbenzene-
1,3-dicarbonitrile oxide, and removing water from the mixture.
Foam compositions, including a latex and a polynitrile oxide such as 2,4,6triethylbenzene-1,3-dicarbonitrile
oxide, or a latex and an epoxy silane, or a latex
and a mixture of the two crosslinkers have been prepared (526). The compositions
may also contain additional components, including Þllers, surfactants, cell
detackiÞers, froth stabilizers, froth boosters, viscosity reducers, and compounds to
improve resilience, and antioxidants. The compositions are particularly useful in
the manufacture of ßooring, wall covering, shoe lining and nonwoven materials.
Nitrile oxide precursors have been prepared by the reaction of an isocyanate
and an alkyl nitroacetate. These precursors release alkanol and carbon dioxide
when heated, to liberate the highly reactive nitrile oxide species. An improved
synthetic procedure has been developed to afford novel cross-linking agents based
on difunctional, trifunctional and aliphatic precursors. Application of these agents
to polymer cross-linking has been demonstrated (527).
Although bisnitrile oxides are generated in situ in the presence of a polymer,
the use of stable bisnitrile oxides prepared beforehand is more attractive owing
to the absence of byproducts. Therefore, special attention has been paid to the
development of syntheses of stable bisnitrile oxides (29–32, 102, 509, 517, 518,
522, 528).
1.4.3. Other Applications of Nitrile Oxides
Using nitrile oxides, various compounds and materials possessing valuable properties
have been prepared. Among them are thin-Þlm resistors useful for a thermal
head and comprising a nitrile oxide, ruthenium and oxygen, a method for manufacturing
the resistor by coating or deposition (529), isoxazole and/or isoxazoline
polyheterocyclic systems like 458, which are useful for development of a new
class of ionophores (530).